Exhaust timing control system for two-cycle engines

Abstract

A system incorporating a pivotally mounted control valve to selectively close the upper portion of an exhaust port in a two-cycle engine including a motor coupled with the valve for driving same. A speed determination means is provided to determine the engine speed relative to a specified value. A drive means rotates the motor in either direction based on the sensing by the speed determination means. A drive current control means detects the magnitude of change of the engine speed and increases or decreases the current supplied to the motor to increase or decrease the speed of change of the control valve.

What is claimed is: 
     
       1. An exhaust timing control system for a two-cycle engine having an exhaust port and a control valve in the exhaust port, comprising a motor coupled with the control valve to position the control valve;   sensor means for sensing the speed of the engine;   drive means coupled with said motor for driving said motor selectively in either direction responsive to said sensing means; and   power control means responsive to said sensor means for selectively increasing power to said motor as the rate of change of the speed of said engine increases and decreasing power to said motor as the rate of change of the speed of said engine decreases.   
     
     
       2. An exhaust timing control system for a two-cycle engine having an exhaust port and a control valve in the upper edge of the exhaust port, comprising: a motor coupled with the control valve to position the control valve to either a first, full-flow position or a second, closed position;   sensor means for sensing the speed of the engine;   drive means coupled with said motor for driving said motor selectively in either direction responsive to said sensor means; and   drive current control means to control the duty ratio of the current supplied to the motor in accordance with the rate of change of speed of the engine.   
     
     
       3. An exhaust timing control system for a two-cycle engine having an exhaust port, comprising: first and second control valves working in unison to selectively adjust the position of the top of the exhaust port;   a motor operatively conencted to one of said control valves to position said control valves; and   motor control means responsive to the speed of said engine for selectively adjusting the speed at which said motor operates, according to rate of change of speed of said engine.   
     
     
       4. The exhaust timing control system of claim 3, in which said motor control means further comprises: speed determination means for determining the speed of said engine and outputting a signal that indicates whether the speed of said engine is below a preselected value;   motor speed selection means responsive to the speed of said engine for outputting a signal that indicates the rate of change of speed of said engine; and   motor drive means operatively connected to both said speed determination means and to said motor speed selection means for adjusting the position and turning direction of said motor according to the speed of said engine, and for adjusting the speed at which said motor turns according to the rate of change of speed of said engine.   
     
     
       5. The exhaust timing control system of claim 4, in which said speed determination means outputs a second signal which is the compliment of said signal. 
     
     
       6. The exhaust timing control system of claim 4, in which said second control valve is spring-biased to contact said first control valve. 
     
     
       7. An exhaust timing control system for a two-cycle engine having an exhaust port, comprising: a first control valve in said exhaust port;   a second control valve in said exhaust port spring-biased to contact said first control valve;   a motor operatively connected to said first control valve to selectively position said first and second control valves in unison;   a drive circuit operatively connected to said motor for selecting the position of said motor as a function of the speed of said engine, and for selectively adjusting the speed at which said motor turns as a function of the rate of change of speed of said engine.   
     
     
       8. The exhaust timing control system of claim 7, further comprising: speed determination means operatively connected to said drive circuit for inputting a plurality of signals to said drive circuit, which signals indicate whether the speed of said engine is below a predetermined value; and   a drive control circuit for inputting to said drive circuit a signal indicating the rate of change of speed of said engine.